What are the critical mesh issues responsible for errors converting mesh to solid body

[hz357NCXK5]

Goal: I need to convert meshes to solid bodies for simulations. The simulation software won't accept T-spline so it has to be converted to BRep.

Mesh issues: ideally, we'd want perfect mesh for solid body conversion. But I created the gyroid meshes from volumetric lattice plugin in Fusion - there are many issues with it, including intersecting faces, zero faces, zero edges, non-flat faces, thin faces, sharp edges, overhang faces (according to Blender 3D printing toolbox). It is impossible to fix all of them manually all at the same time, and I want to know which ones I should prioritise even though I have to compromise on the geometry a little bit.

Question: which mesh issues are critical for failed the solid body conversion? Specifically, which ones are responsible for T-spline conversion, and which ones for T-spline to BRep?

What I learned so far: the conversion failure log has not been consistent.

1. mesh to T-spline

Sometimes, the error log would specify the failure to T-spline is due to intersecting faces, but sometimes the conversion to T-spline is fine with the intersecting faces present. Most of the time, the error log for mesh to t-spline would be "try generating face groups beforehand or direct edit" without pinpointing the mesh issue.

2. tspline to brep

The intersecting faces would be highlighted. But why was it converted from mesh to t-spline when intersecting faces are there in the first place?

[TrippyLighting]

I previously  tried to convert a gyroid lattice mesh into an acceptable T-Spline with the method available in Fusion (Organic mesh conversion) and external tools, such as Instant Meshes, or the Remesher in Blender 4.2. None of those attempts have resulted in a successful solid body.

My conclusion, the lattice tools Fusion are only useful for additive manufacturing workflows and noting else! 

You are likely better off manually modeling a Gyroid in Blender, for example and modify it to your requirements.

Then export the resulting "clean" quad-mesh into Fusion and convert it into a T-Spline and then BRep.

That BRep you can then use to model the final geometry.